Generally, eyeglass lenses are subjected to working of the external shape so as to match the shape of eyeglass frames selected by the customer at a retail shop, and are then placed in the eyeglass frames and handed over to the customer. Working machines that are used to perform such working of the external circumference of the lens are called lens edging machines (edgers, outer edge working machines, or the like). In commonly used lens edging machines, working of the external shape is accomplished by grinding the outer edge of the lens with a grinding tool while the eyeglasses are clamped by a working shaft.
A schematic diagram of this working method is shown in FIG. 6. The lens 21 that is to be worked is first fastened to a locking cap 22 made of plastic by a piece of two-sided adhesive tape 23. Specifically, this two-sided adhesive tape 23 is bonded beforehand to the locking cap 22, and the other side of the tape is bonded to surface of the lens 21 that is to be worked, so that the lens 21 that is to be worked is fastened to the locking cap 22. Then, this locking cap 22 is fastened to an upper-side lens working shaft 24.
Next, this lens 21 that is to be worked is fastened in place by being clamped between a lower-side lens working shaft 25 and the locking cap 22. In this state, a grinding tool 26 is caused to move along the outer circumference of the lens 21 that is to be worked while this grinding tool 26 is rotated, and working of the outer circumference of the lens 21 that is to be worked is performed. There are also cases in which such lens edging is performed at the maker's factory rather than at a retail shop.
In recent years, eyeglass lenses in which the surfaces of the eyeglass lenses are coated with an oil-repellent coating have been marketed. Such lenses tend to resist the adhesion of contaminants to the surface, and are therefore favorably evaluated by eyeglass users. However, during lens edging, since the frictional resistance of the surface is low, the following problem arises in cases where a holding method for conventional eyeglass lenses that do not have an oil-repellent coating is used: namely, the lens working shaft and the lens axis tend to shift during working, so that there may be cases in which the working of the external shape cannot be accurately performed.